Report tax evasion? Or not?

So my girlfriend moved to Oklahoma, and even though we are no longer together, we are still good friends and talk all the time. She was recently laid off/ fired from her job at an ATV shop because her boss decided that she wasnt pretty enough. When I said he cant do that she said that he can because she wasnt ever actually on an employee list or the company's pay roll, and that he paid her, along with her mother, and several other colleagues under the table, aka back door cash. So I suggested that she report him to the IRS tax evasion or what have you, but she doesnt want to, afraid I guess. So I offered to report him for her, but I don't know how nor would I have any sort of reputable evidence if I did, after all she doesnt want to be fined or imprisoned for getting paid under the table kind of thing. So i am kind of at a loss, so I figured I could ask other people's opinions.... So Ideas anyone? All will be greatly appreciated.